Conventional control devices that control controlled devices such as industrial machines include programmable controllers (PLCs) and microcomputer control devices. These control devices are in some cases equipped with a display device that collects information in the internal memory in the control device and information in an I/O signal and displays it so that the operator can check operating information on the controlled device and the like and operate the control device itself.
Examples of a display device connected to a PLC include a programmable display (for example, see Patent Literature 1). The programmable display collects bitwise information in the data memory or the like, which is information on the operating state of the controlled device, and numerical information, such as the number of products, from the PLC via a serial communication port that is called an upper link unit or the like. Then, the programmable display displays and outputs the information on a touch panel in a form based on the HMI display data programmed therein in advance. Moreover, the programmable display can receive an input for operating the values in the data memory of the PLC via the touch panel and update the values in the data memory of the PLC on the basis of the received input.